Electric bicycle power-assisted sensor applied to an intelligent electric power-assist bicycle, is one of the core components of an intelligent electric bicycle. Now the commonly used electric bicycle power-assisted sensor has following several schemes: (1) A speed-type pseudo power-assisted sensor by counting motor pulses or central shaft pulses, increases an output of the motor accordingly by detecting an actual speed of the bicycle. (2) A set of elastic elements are mounted between a central shaft and a chainwheel or between a motor and a freewheel, utilizing a slip displacement of the elastic element after deforming under force to push corresponding mechanical action, producing physical quantity variations, such as magnetic field, quantity of light and so on, with some static sensing device, which is converted to electric quantity to detect a pedalling force of a rider. (3) a set of elastic elements is mounted between a central shaft and a chainwheel or between a motor and a freewheel, and pulse generating devices are mounted at both ends of the elastic elements, utilizing a slip displacement of the elastic element after deforming under force to produce a phase difference between two pulse trains, which converted via a phase discrimination circuit to detect a pedalling force. (4) a deformation body is disposed between a rotational central shaft and a sprocket bracket, is directly adhered to a strain gauge and is arranged with an amplification circuit, which is connected with the outer part using a slip ring and an electric brush. (5) a deformation body is disposed between a rotational central shaft and a sprocket bracket, on which a special material part is adhered, which produce permeance variation under force, causing a inductance variation of a coil assembly which is matched with it but does not rotate with it, converting into corresponding electric quantity by way of detecting a inductance or coupling coefficient. (6) an activity pinch roller is intentionally mounted on a chain major loop, detecting a displacement produced by the pinch roller under a chain tension, producing physical quantity variations, such as magnetic field, quantity of light and so on, with some static sensing device, which is converted to electric quantity to detect a pedalling force of a rider by a linearization conversion. In the above-mentioned six categories, the first one is simple, inexpensive and does not reflect reality, and is not easy to use when in heavy load, against the wind and go up the slope. An advantage of the other five ones is: all can meet usage requirements but each has its disadvantage, and common points are: the volume is large, the price is high, the structure is complex, the precision is low, the reliability is not enough, manufacture and assembling work are difficult.
An CN patent application number CN200710006002.1, entitled a scheme of electric bicycle power-assisted sensor utilizing a central shaft supporting piece to deform, provides a simple structured, relatively practical scheme for detecting a pedalling force. However, because its principle is achieved actually through measuring a deformation of the a strain sleeve caused by the chain tension, obtaining an equal pedalling force through detecting a strain gauge adhered to a strain sleeve, the structure inevitably can cause the central shaft slightly shake front and back, which spoils the riding feel and is of low practical use value.
In conclusion, people urgently need a central shaft torque sensing system that directly transmits a pedalling force to a strain sleeve. Wherein, what is reflected by a torque sensor on the strain sleeve is an actual pedalling force, the measurement of which is accurate, thereby preventing a phenomenon of unbalanced left/right foot detection during measurement by a torque sensing system.